The use of chlorides for the oxidation, solubilization, and recovery of Cu from its secondary or primary sulphide concentrated ore, such as chalcopyrite, from mixed concentrates or from mattes, has been studied and proposed for more than one hundred years to overcome the pyrometallurgical process, that has a serious impact on the environment.
Leaching using chlorides, in particular FeCl.sub.3 and CuCl.sub.2, is by now acknowledged as a very efficient method for the production of concentrated solutions from which to extract Cu directly.
Even with the more refractory sulphides, such as chalcopyrite, the extraction yields are high. The sulphur is produced mostly in elemental form and therefore the conditions exist for a large scale application of this technology.
Despite this, industrial experience has so far been a total failure.
To better understand the reasons it is necessary to examine the characteristics of the most common processes. The Canmet, Minemet Recherche, Broken Hill processes combine leaching using CuCl.sub.2 at atmospheric pressure, with solvent extraction of copper from chloride solution and Cu electrowinning from sulphuric baths.
The Cymet process (U.S. Pat. No. 3,901,776) uses a mixture of FeCl.sub.3 and CuCl.sub.2 as the leaching medium. The CuCl obtained is precipitated from the solution and reduced to Cu metal by using a flow of hydrogen in a fluid bed reactor.
The Duval Clear process and the U.S.B.M. process also use leaching medium based on CuCl.sub.2 and FeCl.sub.3 to produce a CuCl solution that is electrolysed in a diaphragm cell.
The Cu, which is deposited in incoherent form, is removed continuously.
The CuCl.sub.2 is regenerated in the anodic compartment. The purity of the copper produced in this way is insufficient and further electrolytic purification is required.
The Dextec process causes anodic dissolution of the Cu in presence of oxidants. The reaction takes place in a diaphragm cell; the copper sponge, containing the impurities of the starting material, is deposited in the cathode compartment.
The Elkem process leaches the mixed concentrates of Cu with Zn and Pb in a ferric and cupric chloride solution, which operates in counter-current. Cu is recovered in sponge form by electrowinning. In a recent modification of the process there is a production of a CuCl.sub.2 solution, from which the copper is separated by solvent extraction before the electrowinning stage, thereby improving the quality of the Copper produced.
In this process Zn is extracted from the leaching solution using tributylphosphate. Pb is separated as PbCl.sub.2. The process is very complicated: there are problems with the solvent extraction circuits and the physical form of the metals obtained is unsuitable for direct sale, without further processing.
The Cuprex process uses a solution based on NaCl with FeCl.sub.3 to dissolve the copper sulphides, obtaining a CuCl.sub.2 solution. The Cu is extracted using solvents in a 3 stage extraction that operates in counter-current.
Stripping from the solvent is performed using water, producing a concentrated solution of CuCl.sub.2 which is transferred to the electrolytic diaphragm cell. The copper produced is in a sponge, or granular form (that is a commercial cathode) and the process operations are rather complex.
The Intec process performs leaching using an oxidising solution of chlorides containing bromine chloride. After the solution purification using lime, copper is electrolitically extracted in granular form in an ion-selective membrane cell. The copper produced, even though of good quality, is not saleable without undergoing further treatment which transforms it into a finished product.
Among all these processes and the numerous patents having the same goal only Clear process has achieved industrial scale application and produced 32.000 t Cu/year for a certain period.
However, it too had to be shut-down for various technical and economical reasons.
The chloride hydrometallurgy has successfully overcome the drawback of leaching Cu sulphide concentrated ore, but, anyway, has not yet found the complete solution to produce copper cathodes of acceptable quality, with economic costs that are competitive with pyrometallurgy.
The primary purpose of this invention is to provide a process to produce copper in the form of thick, compact, smooth surface and high purity cathodes (at least 99.99%) from Cu sulphide concentrated ore, from copper mattes and from precipitated copper sulphides. In addition to the copper having the characteristics detailed above, according to the purposes of the invention, sulphur in an elementary form must be produced.